Technical Abstract:
Soil organic matter (SOM) has important beneficial properties related to soil stability. Objectives were to determine effect of tillage on composition of SOM and stability of soil aggregates. Measurements were made on two adjacent farms having a clay loam soil under a corn-soybean rotation in eastern South Dakota. Soil was collected from the top 50 mm of no tillage (NT) and conservation tillage (CT) farms. Primary tillage on CT was chisel plow. A rotary sieve was used to separate samples into aggregate classes. Group 1 was soil less than 0.4 mm, group 2 was 0.4-0.8 mm, group 3 was 0.8-2 mm, group 4 was 2-6 mm, group 5 was 6-19 mm, and group 6 was soil greater than 19 mm. Water stability of dry and pre-moistened aggregates were determined by wet-sieving. Total soil carbon (C), immunoreactive total glomalin (IRTG), basidiomycete fungi (BF), and humic acid (HA) were measured. Average C and IRTG was 4% and 46% greater under NT, compared with CT, respectively. BF was 20% greater under NT compared with CT. Group 5 aggregates had 17% more HA compared to group 3. Water stability of dry aggregates from NT was twice that of CT. Soil aggregates from NT resisted breakdown (dry and wet sieving) compared with aggregates from CT. Differences in properties among aggregates show that SOM is not uniformly distributed among aggregate groups and that soil aggregation improved under no tillage.